Kinda depends on the Media Player your using. WMP Sucks but you can try adding the following Codex.

For XP this codec pac is very good
Download XP Codec Pack 2.0.8 - XP Codec Pack is one of the most complete codec pack
Or for Vista this pac
Vista Codec Package v4.4.7 Beta 4a (freeware)

K-Lite Mega Codec Pack


I will suggest trying VLC Media Player. See VLC Player within this thread.

CODECs list for Movies/Audio/ Alternate players / Video help forums/ video-mp3 fixers

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